Network Working Group Y. Rekhter
Request for Comments: 2073 cisco
Category: Standards Track P. Lothberg
STUPI.AB
R. Hinden
Ipsilon Networks
S. Deering
Xerox PARC
J. Postel
ISI
Editors
January 1997
An IPv6 Provider-Based Unicast Address Format
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
1.0 Introduction
This document defines an IPv6 provider-based unicast address format
for use in the Internet. The address format defined in this document
is consistent with the "IPv6 Addressing Architecture" [ARCH] and the
"An Architecture for IPv6 Unicast Address Allocation" [ALLOC], and is
intended to facilitate scalable Internet routing.
The unicast address format defined in this document doesn't preclude
the use of other unicast address formats.
2.0 Overview of the IPv6 Address
IPv6 addresses are 128-bit identifiers for interfaces and sets of
interfaces. There are three types of addresses: Unicast, Anycast,
and Multicast. This document defines a specific type of Unicast
address.
In this document, fields in addresses are given specific names, for
example "subscriber". When this name is used with the term "ID" (for
"identifier") after the name (e.g., "subscriber ID"), it refers to
the contents of the named field. When it is used with the term
"prefix" (e.g., "subscriber prefix") it refers to all of the address
up to and including this field.
Rekhter, et. al. Standards Track [Page 1]RFC 2073 IPv6 Provider-Based Unicast Address Format January 1997
The specific type of an IPv6 address is indicated by the leading bits
in the address. The variable-length field comprising these leading
bits is called the Format Prefix (FP).
This document defines an address format for the 010 (binary) Format
Prefix for Provider-Based Unicast addresses. The same address format
could be used for other Format Prefixes, as long as these Format
Prefixes also identify IPv6 unicast addresses. Only the "010" Format
Prefix is defined here.
3.0 IPv6 Provider-Based Unicast Address Format
This document defines an address format for the IPv6 provider-based
unicast address assignment. It is expected that this address format
will be widely used for IPv6 nodes connected to the Internet.
The address format defined in this document conforms to the
"Architecture for IPv6 Unicast Address Allocation" [ALLOC].
Specifically, the format is designed to support aggregation of
network layer reachability information at multiple levels of routing
hierarchy.
For addresses of the format described in this document the address
administration is organized into a three level hierarchy -- registry,
provider, and subscriber. The address format defined here allows
flexible address allocation at each level of the address
administration hierarchy in such a way as to support a wide spectrum
of demands for address allocation.
This document assumes that the Internet routing system doesn't make
any assumptions about the specific structure and semantics of an IPv6
address, except for the structure and semantics of the Format Prefix
part of the address, and the use of the "longest prefix match"
algorithm (on arbitrary bit boundaries) for making a forwarding
decision.
The address format defined in this document is intended to facilitate
scalable Internet-wide routing that does not impose any constraints
on connectivity among the providers, as well as among the providers
and subscribers.
Rekhter, et. al. Standards Track [Page 2]RFC 2073 IPv6 Provider-Based Unicast Address Format January 19973.1 Provider-Based Unicast Address Structure
For the purpose of address allocation, the address format defined in
this document consists of the following parts: Format Prefix,
Registry ID, Provider ID, Subscriber ID, and an Intra-Subscriber